Docosatetraenoic acid in endothelial cells: formation, retroconversion to arachidonic acid, and effect on prostacyclin production

The imperative of arachidonic acid in early human development

This review is about the role of arachidonic acid (ArA) in foetal and early growth and development. In 1975 and '76, we reported the preferential incorporation of ArA into the developing brain of rat pups, its conservation as a principal component in the brains of 32 mammalian species and the high proportion delivered by the human placenta for foetal nutrition, compared to its parent linoleic acid (LA). ArA is quantitatively the principal acyl component of membrane lipids from foetal red cells, mononuclear cells, astrocytes, endothelium, and placenta. Functionally, we present evidence that ArA, but not DHA, relaxes the foetal mesenteric arteries. The placenta biomagnifies ArA, doubling the proportion of the maternal level in cord blood. The proportions of ArA and its allies (di-homo-gamma-linolenic acid (DGLA), adrenic acid and ω6 docosapentaenoic acid) are similar or higher than the total of ω3 fatty acids in human milk, maintaining the abundant supply to the developing infant. Despite the evidence of the importance of ArA, the European Food Standard Agency, in 2014 rejected the joint FAO and WHO recommendation on the inclusion of ArA in infant formula, although they recommended DHA. The almost universal dominance of ArA in the membrane phosphoglycerides during human organogenesis and prenatal growth suggests that the importance of ArA and its allies in reproductive biology needs to be re-evaluated urgently.

Alterations in Faecal and Serum Metabolic Profiles in Patients with Neovascular Age-Related Macular Degeneration

Neovascular age-related macular degeneration (nAMD) is a common and multifactorial disease in the elderly that may lead to irreversible vision loss; yet the pathogenesis of AMD remains unclear. In this study, nontargeted metabolomics profiling using ultra-performance liquid chromatography coupled with Q-Exactive Orbitrap mass spectrometry was applied to discover the metabolic feature differences in both faeces and serum samples between Chinese nonobese subjects with and without nAMD. In faecal samples, a total of 18 metabolites were significantly altered in nAMD patients, and metabolic dysregulations were prominently involved in glycerolipid metabolism and nicotinate and nicotinamide metabolism. In serum samples, a total of 29 differential metabolites were founded, involved in caffeine metabolism, biosynthesis of unsaturated fatty acids, and purine metabolism. Two faecal metabolites (palmitoyl ethanolamide and uridine) and three serum metabolites (4-hydroxybenzoic acid, adrenic acid, and palmitic acid) were selected as potential biomarkers for nAMD. Additionally, the significant correlations among dysregulated neuroprotective, antineuroinflammatory, or fatty acid metabolites in faecal and serum and IM dysbiosis were found. This comprehensive metabolomics study of faeces and serum samples showed that alterations in IM-mediated neuroprotective metabolites may be involved in the pathophysiology of AMD, offering IM-based nutritional therapeutic targets for nAMD.

Multimodal plasma metabolomics and lipidomics in elucidating metabolic perturbations in tuberculosis patients with concurrent type 2 diabetes

Type 2 diabetes mellitus (DM) poses a major burden for the treatment and control of tuberculosis (TB). Characterization of the underlying metabolic perturbations in DM patients with TB infection would yield insights into the pathophysiology of TB-DM, thus potentially leading to improvements in TB treatment. In this study, a multimodal metabolomics and lipidomics workflow was applied to investigate plasma metabolic profiles of patients with TB and TB-DM. Significantly different biological processes and biomarkers in TB-DM vs. TB were identified using a data-driven, knowledge-based framework. Changes in metabolic and signaling pathways related to carbohydrate and amino acid metabolism were mainly captured by amide HILIC column metabolomics analysis, while perturbations in lipid metabolism were identified by the C18 metabolomics and lipidomics analysis. Compared to TB, TB-DM exhibited elevated levels of bile acids and molecules related to carbohydrate metabolism, as well as the depletion of glutamine, retinol, lysophosphatidylcholine, and phosphatidylcholine. Moreover, arachidonic acid metabolism was determined as a potential important factor in the interaction between TB and DM pathophysiology. In a correlation network of the significantly altered molecules, among the central nodes, chenodeoxycholic acid was robustly associated with TB and DM. Fatty acid (22:4) was a component of all significant modules. In conclusion, the integration of multimodal metabolomics and lipidomics provides a thorough picture of the metabolic changes associated with TB-DM. The results obtained from this comprehensive profiling of TB patients with DM advance the current understanding of DM comorbidity in TB infection and contribute to the development of more effective treatment.

Potential Antihypertensive Mechanisms of the Egg White-Derived Peptide QIGLF in Spontaneously Hypertensive Rats Revealed Using Untargeted Serum Metabolomics

The angiotensin-converting enzyme (ACE) inhibitory peptide QIGLF derived from egg white was shown to have significant in vivo antihypertensive effects in our previous study, but the intervention mechanisms at the metabolic level are still unclear. The UPLC-QTOF/MS-based untargeted metabolomics approach was used to clarify the potential antihypertensive mechanisms of QIGLF in the serum of spontaneously hypertensive rats (SHRs). Multivariate statistical analysis showed a clear difference in the metabolite profiles between the QIGLF and model groups. The results suggested that eight potential biomarkers were identified, that is, adrenic acid, ursodeoxycholic acid, glycocholic acid, taurocholic acid, tryptophan, acetylindoxyl, tyrosine, and 2-phenylethanol, which were mainly involved in aromatic amino acid biosynthesis and metabolism, biosynthesis of bile acid, and biosynthesis of unsaturated fatty acids. QIGLF might exert antihypertensive effects by improving endothelial dysfunction. This study provides a theoretical basis for future research and application of ACE inhibitory peptides in the prevention and improvement of hypertension.

Soybean oil lowers circulating cholesterol levels and coronary heart disease risk, and has no effect on markers of inflammation and oxidation

To reduce risk of coronary heart disease, replacement of saturated fats (SFAs) with polyunsaturated fats (PUFA) is recommended. Strong and concordant evidence supports this recommendation, but controversy remains. Some observational studies have reported no association between SFAs and coronary heart disease, likely because of failure to account for the macronutrient replacing SFAs, which determines the direction and strength of the observed associations. Controversy also persists about whether ω-6 (nω-6) PUFA or a high dietary ratio of nω-6 to ω-3 (nω-3) fatty acids leads to proinflammatory and pro-oxidative states. These issues are relevant to soybean oil, which is the leading edible oil consumed globally and in the United States. Soybean oil accounts for over 40% of the US intake of both essential fatty acids. We reviewed clinical and epidemiologic literature to determine the effects of soybean oil on cholesterol levels, inflammation, and oxidation. Clinical evidence indicates that soybean oil does not affect inflammatory biomarkers, nor does it increase oxidative stress. On the other hand, it has been demonstrated that when dietary SFAs are replaced with soybean oil, blood cholesterol levels are lowered. Regarding the nω-6:nω-3 dietary ratio, health agencies have consistently rejected the importance of this ratio, instead emphasizing the importance of consuming sufficient amounts of each type of fat. Thus, several lines of evidence indicate that soybean oil can positively contribute to overall health and reduction of risk of coronary heart disease.

Adrenic Acid-Derived Epoxy Fatty Acids Are Naturally Occurring Lipids and Their Methyl Ester Prodrug Reduces Endoplasmic Reticulum Stress and Inflammatory Pain

Adrenic acid (AdA, 22:4) is an ω-6 polyunsaturated fatty acid (PUFA), derived from arachidonic acid. Like other PUFAs, it is metabolized by cytochrome P450s to a group of epoxy fatty acids (EpFAs), epoxydocosatrienoic acids (EDTs). EpFAs are lipid mediators with various beneficial bioactivities, including exertion of analgesia and reduction of endoplasmic reticulum (ER) stress, that are degraded to dihydroxy fatty acids by the soluble epoxide hydrolase (sEH). However, the biological characteristics and activities of EDTs are relatively unexplored, and, alongside dihydroxydocosatrienoic acids (DHDTs), they had not been detected in vivo. Herein, EDT and DHDT regioisomers were synthesized, purified, and used as standards for analysis with a selective and quantitative high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. Biological verification in AdA-rich tissues suggests that basal metabolite levels are highest in the liver, with 16,17-EDT concentrations consistently being the greatest across the analyzed tissues. Enzyme hydrolysis assessment revealed that EDTs are sEH substrates, with greatest relative rate preference for the 13,14-EDT regioisomer. Pretreatment with an EDT methyl ester regioisomer mixture significantly reduced the onset of tunicamycin-stimulated ER stress in human embryonic kidney cells. Finally, administration of the regioisomeric mixture effectively alleviated carrageenan-induced inflammatory pain in rats. This study indicates that EDTs and DHDTs are naturally occurring lipids, and EDTs could be another therapeutically relevant group of EpFAs.

Anti-Inflammatory and Proresolving Effects of the Omega-6 Polyunsaturated Fatty Acid Adrenic Acid

Polyunsaturated fatty acids (PUFAs) and their metabolites are potent regulators of inflammation. Generally, omega (n)-3 PUFAs are considered proresolving whereas n-6 PUFAs are classified as proinflammatory. In this study, we characterized the inflammatory response in murine peritonitis and unexpectedly found the accumulation of adrenic acid (AdA), a poorly studied n-6 PUFA. Functional studies revealed that AdA potently inhibited the formation of the chemoattractant leukotriene B₄ (LTB₄), specifically in human neutrophils, and this correlated with a reduction of its precursor arachidonic acid (AA) in free form. AdA exposure in human monocyte-derived macrophages enhanced efferocytosis of apoptotic human neutrophils. In vivo, AdA treatment significantly alleviated arthritis in an LTB₄-dependent murine arthritis model. Our findings are, to our knowledge, the first to indicate that the n-6 fatty acid AdA effectively blocks production of LTB₄ by neutrophils and could play a role in resolution of inflammation in vivo.

The Contribution of Cytosolic Group IVA and Calcium-Independent Group VIA Phospholipase A2s to Adrenic Acid Mobilization in Murine Macrophages

Adrenic acid (AA), the 2-carbon elongation product of arachidonic acid, is present at significant levels in membrane phospholipids of mouse peritoneal macrophages. Despite its abundance and structural similarity to arachidonic acid, very little is known about the molecular mechanisms governing adrenic acid mobilization in cells of the innate immune system. This contrasts with the wide availability of data on arachidonic acid mobilization. In this work, we used mass-spectrometry-based lipidomic procedures to define the profiles of macrophage phospholipids that contain adrenic acid and their behavior during receptor activation. We identified the phospholipid sources from which adrenic acid is mobilized, and compared the data with arachidonic acid mobilization. Taking advantage of the use of selective inhibitors, we also showed that cytosolic group IVA phospholipase A₂ is involved in the release of both adrenic and arachidonic acids. Importantly, calcium independent group VIA phospholipase A₂ spared arachidonate-containing phospholipids and hydrolyzed only those that contain adrenic acid. These results identify separate mechanisms for regulating the utilization of adrenic and arachidonic acids, and suggest that the two fatty acids may serve non-redundant functions in cells.

Sperm motility and lipid composition in internally fertilizing ocellate river stingray Potamotrygon motoro

All extant groups of Elasmobranches have internal fertilization and the structure of the male reproductive organs is very specific: sperm passes from the internal organs via the cloaca, but the male copulating organ (clasper) is distant from the cloaca. This suggests that sperm can contact the surrounding medium before fertilization. Because of this involvement with the environment, external signaling in sperm motility activation could occur in these species even though their fertilization mode is internal. In this case, spermatozoa of Elasmobranches should hypothetically possess a specific structure and membrane lipid composition which supports physiological functions of the sperm associated with environmental tonicity changes occurring at fertilization. Additionally, sperm motility properties in these taxa are poorly understood. The current study examined sperm lipid composition and motility under different environmental conditions for the ocellate river stingray, Potamotrygon motoro, an endemic South America freshwater species. Sperm samples were collected from six mature males during the natural spawning period. Sperm motility was examined in seminal fluid and fresh water by light video microscopy. Helical flagellar motion was observed in seminal fluid and resulted in spermatozoon progression; however, when diluted in fresh water, spermatozoa were immotile and had compromised structure. Lipid class and fatty acid (FA) composition of spermatozoa was analyzed by thin layer and gas chromatography. Spermatozoa FAs consisted of 33 ± 1% saturated FAs, 28 ± 1% monounsaturated FAs (MUFAs), and 41 ± 1% polyunsaturated FAs (PUFAs), and a high content of n-6 FAs (32 ± 2%) was measured. These results allowed us to conclude that sperm transfer from P. motoro male into female should occur without coming into contact with the hypotonic environment so as to preserve potent motility. In addition, this unusual reproductive strategy is associated with specific spermatozoa structure and lipid composition. Low level of docosahexaenoic acid and relatively low PUFA/MUFA ratio probably account for the relatively low fluidity of freshwater stingray membrane and can be the main reason for its low tolerance to hypotonicity.

Is essential fatty acid interconversion an important source of PUFA in humans?

Humans can obtain pre-formed long-chain PUFA from the diet and are also able to convert essential fatty acids (EFA) to longer-chain PUFA. The metabolic pathway responsible for EFA interconversion involves alternating desaturation and carbon chain elongation reactions, and carbon chain shortening by peroxisomal β-oxidation. Studies using stable isotope tracers or diets supplemented with EFA show that capacity for PUFA synthesis is limited in humans, such that DHA (22 : 6n-3) synthesis in men is negligible. PUFA synthesis is higher in women of reproductive age compared with men. However, the magnitude of the contribution of hepatic PUFA synthesis to whole-body PUFA status remains unclear. A number of extra-hepatic tissues have been shown to synthesise PUFA or to express genes for enzymes involved in this pathway. The precise function of extra-hepatic PUFA synthesis is largely unknown, although in T lymphocytes PUFA synthesis is involved in the regulation of cell activation and proliferation. Local PUFA synthesis may also be important for spermatogenesis and fertility. One possible role of extra-hepatic PUFA synthesis is that it may provide PUFA in a timely manner to facilitate specific cell functions. If so, this may suggest novel insights into the effect of dietary PUFA and/or polymorphisms in genes involved in PUFA synthesis on health and tissue function.

Effects of in Utero PFOS Exposure on Transcriptome, Lipidome, and Function of Mouse Testis

Transcriptomic and LC-MS/MS-based targeted lipidomic analyses were conducted to identify the effects of in utero PFOS exposure on neonatal testes and its relation to testicular dysfunction in adult offspring. Pregnant mice were orally administered 0.3 and 3 μg PFOS/g body weight until term. Neonatal testes (P1) were collected for the detection of PFOS, and were subjected to omics study. Integrated pathway analyses using DAVID, KEGG, and IPA underlined the effects of PFOS exposure on lipid metabolism, oxidative stress and cell junction signaling in testes. LC-MS/MS analysis showed that the levels of adrenic acid and docosahexaenoic acid (DHA) in testes were significantly reduced in the PFOS treatment groups. A significant linear decreasing trend in eicosapentaenoic acid and DHA with PFOS concentrations was observed. Moreover, LOX-mediated 5-hydroxyeicosatetraenoic acids (HETE) and 15-HETE from arachidonic acid in the testes were significantly elevated and a linear increasing trend of 15-HETE concentrations was detected with doses of PFOS. The perturbations of lipid mediators suggested that PFOS has potential negative impacts on testicular functions. Postnatal analysis of male offspring at P63 showed significant reductions in serum testosterone and epididymal sperm count. This study sheds light into the as yet unrevealed action of PFOS on lipid mediators in affecting testicular functions.

Metabolic fate of docosahexaenoic acid (DHA; 22:6n-3) in human cells: direct retroconversion of DHA to eicosapentaenoic acid (20:5n-3) dominates over elongation to tetracosahexaenoic acid (24:6n-3)

Docosahexaenoic acid (22:6n-3) supplementation in humans causes eicosapentaenoic acid (20:5n-3) levels to rise in plasma, but not in neural tissue where 22:6n-3 is the major omega-3 in phospholipids. We determined whether neuronal cells (Y79 and SK-N-SH) metabolize 22:6n-3 differently from non-neuronal cells (MCF7 and HepG2). We observed that (13) C-labeled 22:6n-3 was primarily esterified into cell lipids. We also observed that retroconversion of 22:6n-3 to 20:5n-3 was 5- to 6-fold greater in non-neural compared to neural cells and that retroconversion predominated over elongation to tetracosahexaenoic acid (24:6n-3) by 2-5-fold. The putative metabolic intermediates, (13) C-labeled 22:5n-3 and (13) C-labeled 24:5n-3, were not detected in our assays. Analysis of the expression of enzymes involved in fatty acid beta-oxidation revealed that MCF7 cells abundantly expressed the mitochondrial enzymes CPT1A, ECI1, and DECR1, whereas the peroxisomal enzyme ACOX1 was abundant in HepG2 cells, thus suggesting that the initial site of 22:6n-3 oxidation depends on the cell type. Our data reveal that non-neural cells more actively metabolize 22:6n-3 to 20:5n-3 via channeled retroconversion, while neural cells retain 22:6n-3.

Chronic Insulin Exposure Induces ER Stress and Lipid Body Accumulation in Mast Cells at the Expense of Their Secretory Degranulation Response

Lipid bodies (LB) are reservoirs of precursors to inflammatory lipid mediators in immunocytes, including mast cells. LB numbers are dynamic, increasing dramatically under conditions of immunological challenge. We have previously shown in vitro that insulin-influenced lipogenic pathways induce LB biogenesis in mast cells, with their numbers attaining steatosis-like levels. Here, we demonstrate that in vivo hyperinsulinemia resulting from high fat diet is associated with LB accumulation in murine mast cells and basophils. We characterize the lipidome of purified insulin-induced LB, and the shifts in the whole cell lipid landscape in LB that are associated with their accumulation, in both model (RBL2H3) and primary mast cells. Lipidomic analysis suggests a gain of function associated with LB accumulation, in terms of elevated levels of eicosanoid precursors that translate to enhanced antigen-induced LTC4 release. Loss-of-function in terms of a suppressed degranulation response was also associated with LB accumulation, as were ER reprogramming and ER stress, analogous to observations in the obese hepatocyte and adipocyte. Taken together, these data suggest that chronic insulin elevation drives mast cell LB enrichment in vitro and in vivo, with associated effects on the cellular lipidome, ER status and pro-inflammatory responses.

Role of cytochrome P450 enzymes in the bioactivation of polyunsaturated fatty acids

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA), such as epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid, serve as second messengers of various hormones and growth factors and play pivotal roles in the regulation of vascular, renal and cardiac function. As discussed in the present review, virtually all of the major AA metabolizing CYP isoforms accept a variety of other polyunsaturated fatty acids (PUFA), including linoleic, eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), as efficient alternative substrates. The metabolites of these alternative PUFAs also elicit profound biological effects. The CYP enzymes respond to alterations in the chain-length and double bond structure of their substrates with remarkable changes in the regio- and stereoselectivity of product formation. The omega-3 double bond that distinguishes EPA and DHA from their omega-6 counterparts provides a preferred epoxidation site for CYP1A, CYP2C, CYP2J and CYP2E subfamily members. CYP4A enzymes that predominantly function as AA ω-hydroxylases show largely increased (ω-1)-hydroxylase activities towards EPA and DHA. Taken together, these findings indicate that CYP-dependent signaling pathways are highly susceptible to changes in the relative bioavailability of the different PUFAs and may provide novel insight into the complex mechanisms that link essential dietary fatty acids to the development of cardiovascular disease.

Adrenic acid metabolites as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the adrenal gland, is identical to arachidonic acid except for 2 additional carbons on the carboxyl end. Adrenic acid is metabolized by cyclooxygenases, cytochrome P450s, and lipoxygenases; however, little is known regarding the role of adrenic acid and its metabolites in vascular tone. Because of its abundance in the adrenal gland, we investigated the role of adrenic acid in vascular tone of bovine adrenal cortical arteries and its metabolism by bovine adrenal zona glomerulosa cells. In adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations, which were inhibited by the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid and the cytochrome P450 inhibitor SKF-525A. The large-conductance calcium-activated potassium channel blocker iberiotoxin or removal of the endothelium abolished these relaxations. Reverse-phase high-pressure liquid chromatography and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from zona glomerulosa cells, including dihomo-epoxyeicosatrienoic acids and dihomo-prostaglandins. In denuded adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations in the presence of zona glomerulosa cells but not in their absence. These relaxations were inhibited by SKF-525A, 14,15-epoxyeicosa-5(Z)-enoic acid, and iberiotoxin. Dihomo-16,17-epoxyeicosatrienoic acid caused concentration-dependent relaxations of adrenal cortical arteries, which were inhibited by 14,15-epoxyeicosa-5(Z)-enoic acid and high potassium. Our results suggest that adrenic acid relaxations of bovine adrenal cortical arteries are mediated by endothelial and zona glomerulosa cell cytochrome P450 metabolites. Thus, adrenic acid metabolites could function as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors in the adrenal cortex and contribute to the regulation of adrenal blood flow.

Metabolomic profiling of a modified alcohol liquid diet model for liver injury in the mouse uncovers new markers of disease

Metabolomic evaluation of urine and liver was conducted to assess the biochemical changes that occur as a result of alcohol-induced liver injury. Male C57BL/6J mice were fed an isocaloric control- or alcohol-containing liquid diet with 35% of calories from corn oil, 18% protein and 47% carbohydrate/alcohol for up to 36 days ad libitum. Alcohol treatment was initiated at 7 g/kg/day and gradually reached a final dose of 21 g/kg/day. Urine samples were collected at 22, 30 and 36 days and, in additional treatment groups, liver and serum samples were harvested at 28 days. Steatohepatitis was induced in the alcohol-fed group since a 5-fold increase in serum alanine aminotransferase activity, a 6-fold increase in liver injury score (necrosis, inflammation and steatosis) and an increase in lipid peroxidation in liver were observed. Liver and urine samples were analyzed by nuclear magnetic resonance spectroscopy and electrospray infusion/Fourier transform ion cyclotron resonance-mass spectrometry. In livers of alcohol-treated mice the following changes were noted. Hypoxia and glycolysis were activated as evidenced by elevated levels of alanine and lactate. Tyrosine, which is required for l-DOPA and dopamine as well as thyroid hormones, was elevated possibly reflecting alterations of basal metabolism by alcohol. A 4-fold increase in the prostacyclin inhibitor 7,10,13,16-docosatetraenoic acid, a molecule important for regulation of platelet formation and blood clotting, may explain why chronic drinking causes serious bleeding problems. Metabolomic analysis of the urine revealed that alcohol treatment leads to decreased excretion of taurine, a metabolite of glutathione, and an increase in lactate, n-acetylglutamine and n-acetylglycine. Changes in the latter two metabolites suggest an inhibition of the kidney enzyme aminoacylase I and may be useful as markers for alcohol consumption.

Metabolism of adrenic acid to vasodilatory 1α,1β-dihomo-epoxyeicosatrienoic acids by bovine coronary arteries

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the vasculature, is produced by a two-carbon chain elongation of arachidonic acid. Despite its abundance and similarity to arachidonic acid, little is known about its role in the regulation of vascular tone. Gas chromatography/mass spectrometric analysis of bovine coronary artery and endothelial cell lysates revealed arachidonic acid concentrations of 2.06 ± 0.01 and 6.18 ± 0.60 μg/mg protein and adrenic acid concentrations of 0.29 ± 0.01 and 1.56 ± 0.16 μg/mg protein, respectively. In bovine coronary arterial rings preconstricted with the thromboxane mimetic U-46619, adrenic acid (10−9–10−5M) induced concentration-related relaxations (maximal relaxation = 83 ± 4%) that were similar to arachidonic acid relaxations. Adrenic acid relaxations were blocked by endothelium removal and the K+channel inhibitor, iberiotoxin (100 nM), and inhibited by the cyclooxygenase inhibitor, indomethacin (10 μM, maximal relaxation = 53 ± 4%), and the cytochrome P-450 inhibitor, miconazole (10 μM, maximal relaxation = 52 ± 5%). Reverse-phase HPLC and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from coronary arteries including dihomo (DH)-epoxyeicosatrienoic acids (EETs) and DH-prostaglandins. DH-EET [16,17-, 13,14-, 10,11-, and 7,8- (10−9–10−5M)] induced similar concentration-related relaxations (maximal relaxations averaged 83 ± 3%). Adrenic acid (10−6M) and DH-16,17-EET (10−6M) hyperpolarized coronary arterial smooth muscle. DH-16,17-EET (10−8–10−6M) activated iberiotoxin-sensitive, whole cell K+currents of isolated smooth muscle cells. Thus, in bovine coronary arteries, adrenic acid causes endothelium-dependent relaxations that are mediated by cyclooxygenase and cytochrome P-450 metabolites. The adrenic acid metabolite, DH-16,17-EET, activates smooth muscle K+channels to cause hyperpolarization and relaxation. Our results suggest a role of adrenic acid metabolites, specifically, DH-EETs as endothelium-derived hyperpolarizing factors in the coronary circulation.

Conversion of arachidonic acid to tetradecadienoic acid by peroxisomal oxidation

Human skin fibroblasts convert [5,6,8,9,11,12,14,15-3H]arachidonic acid to two radiolabeled polar metabolites that accumulate in the culture medium. Previous studies identified the most abundant of these products as 4,7,10-hexadecatrienoic acid (16:3). We have now identified the second metabolite as 5,8-tetradecadienoic acid (14:2). Fibroblasts deficient in mitochondrial long-chain acyl coenzyme A dehydrogenase produce increased amounts of 14:2 from arachidonic acid. By contrast, Zellweger fibroblasts which are deficient in peroxisomal beta-oxidation do not convert arachidonic acid to either 14:2 or 16:3. These results demonstrate that 14:2 can be synthesized from arachidonic acid, that this oxidative process occurs in the peroxisomes, and that the pathway does not function in Zellweger's syndrome and similar diseases where there is a genetic deficiency in peroxisomal beta-oxidation.

Diversity in the ability of cultured cells to elongate and desaturate essential (n-6 and n-3) fatty acids

Essential fatty acids (EFAs) cannot be synthesized by mammalian cells. Once taken in with the diet, they can undergo desaturations/saturations and chain elongations/shortenings to yield a variety of polyunsaturated fatty acids of the same family. Cells in vitro from a variety of tissues are capable of processing EFAs to varying extents. Conversion of the parent EFAs, linoleic (LA, n-6) and alpha-linolenic (LNA, n-3) acids, to the 20-carbon polyunsaturated fatty acids, arachidonic (AA, n-6) and eicosapentanoic (EPA, n-3), requires chain elongation and delta 6 and delta 5 desaturations. AA and EPA are required by many tissues for optimal biological function and are precursors of biologically active eicosanoid hormones. All cultured cells are able to elongate exogenous LA and LNA, and most can perform delta 5 desaturation, so delta 6 desaturation is the limiting step in AA and EPA production. Longer fatty acids that have more double bonds than AA or EPA are less frequently produced due to a deficiency in delta 4 desaturating ability. The process of retroconversion (chain shortening) is less extensively studied, but evidence from a variety of cells suggests that this type of metabolic conversion is normally active. The example of MCF-7 (human breast cancer cell line) and MCF-10A cells (human noncancerous breast cell line) is discussed in order to emphasize the diversity in EFA processing ability of cultured cells. Under identical culture conditions, MCF-10A cells perform extensive desaturations, elongations, and retroconversions, whereas MCF-7 cells can only elongate and retroconvert exogenous EFAs. Given the great diversity in the ability of cultured cells to process EFAs, no conclusions can be drawn regarding the mechanisms responsible for the effects of exogenous EFAs on a particular cell until that cell's EFA processing patterns have been evaluated.

Priming effect of adrenic acid (22:4(n-6)) on tissue factor activity expressed by thrombin-stimulated endothelial cells

Tissue factor (TF) which initiates clotting process can be expressed by stimulated endothelial cells (EC). TF is an apolipoprotein requiring an association with phospholipids (PL) in order to become active. Also PL constitute an important storage pool of polyunsaturated fatty acids (PUFAs) in EC which can be modulated by diet or cell medium supplementation. In order to test the effect of such manipulation upon TF activity, we have pre-enriched human EC cultures with different fatty acids of nutritional interest. TF was evaluated after 4 h of thrombin stimulation by using a chromogenic method. Without additional stimulating agents, these acids have no effect on the basal level of TF. Eicosapentaenoic and docosapentaenoic acids appeared to be ineffective at the stimulated TF level. Only adrenic acid (22:4(n-6)) has been found to significantly enhance TF activity of thrombin-stimulated endothelial cells. Other TF inducers were also tested after 22:4(n-6) enrichment. An increase tendency of TF expression was found only with tumor necrosis factor, whereas interleukin-1 beta, lipopolysaccharide and especially phorbol myristate acetate stimulations were not significantly modified. The priming effect of adrenic acid on thrombin stimulated TF expression might involve alterations of signal transduction pathways rather than modifications of apolipoprotein III environment. Adrenic acid, which is a prostacyclin inhibitor, appears to be potential prothrombotic agent.

Condensation activity for polyunsaturated fatty acids with malonyl-CoA in rat brain microsomes. Characteristics and developmental change

Condensation activities for gamma-linolenic acid (18:3(n-6)), octadecatetraenoic acid (18:4(n-3)) and eicosapentaenoic acid (20:5(n-3)) with malonyl-CoA were measured and compared with the condensation activities for 16:0-CoA, 18:1-CoA, 18:2(n-6)-CoA and 18:3(n-3)-CoA in rat brain microsomes of various ages. The age-dependence of condensation activities for 18:3(n-6), 18:4(n-3) and 20:5(n-3) showed a maximum at 1- to 2-month-old and were still higher at 3-month-old 2- to 3-fold than the activities in microsomes of pups. Conversely, the age-dependence of condensation activity for 16:0-CoA showed a peak around 1 month-old, but decreased at 3-month-old to the level of the activities in pups. The condensation activity for 20:5(n-3) was inhibited by 18:3(n-6) or 18:4(n-3) and the inhibition was not competitive. The condensation of 18:3(n-6) was also inhibited by 18:4(n-3) in the same manner. A physiological implication of the inhibition system at the substrate level was discussed.

Retroconversion and delta 4 desaturation of docosatetraenoate (22:4(n-6)) and docosapentaenoate (22:5(n-3)) by human cells in culture

This study has investigated the metabolic modification of [3-14C]docosatetraenoate (22:4(n-6)) and [3-14C]docosapentaenoate (22:5(n-3)) by human cells in culture. Fetal skin fibroblasts converted as much as 20% of the incorporated [14C]22:4(n-6) to [14C]20:4(n-6) within 6 h and 41% within 48 h. Retroconversion of incorporated [14C]22:5(n-3) was less than 13% at all time points. Chain shortening of [14C]22:4(n-6) was also 2-6-fold greater than that of [14C]22:5(n-3) in retinoblastoma and vascular endothelial cells. Fibroblasts, vascular endothelial cells and retinoblastoma cells all elongated substantially more [14C]eicosapentaenoate than [14C]arachidonate to the respective C22 fatty acids. Within 3-4 days, fibroblasts incubated with either [14C]20:5(n-3) or [14C]22:5(n-3) had the same ratio of radiolabeled C22:C20 fatty acids in cellular glycerolipids. By contrast, the cells incubated with [14C]22:4(n-6) or [14C]20:4(n-6) did not reach a common C22/C20 equilibrium by 5 days. Although fibroblasts were found to desaturate [14C]22:5(n-3), a substantial lag time was observed; [14C]22:6(n-3) was 2% at 48 h and 20% at 96 h. By contrast, synthesis of [14C]22:6(n-3) by retinoblastoma cells was 51% within 6 h and greater than 90% at 96 h. Desaturation of [14C]22:4(n-6) was observed in retinoblastoma cells, but not in fibroblasts. These results thus suggest that the ratio of C22C20 polyunsaturated fatty acids in cells is regulated by the relative rates of retroconversion and chain elongation, with the net effect of the two processes favoring C20 for n-6 and C22 for the n-3 fatty acids. Furthermore, although fibroblasts desaturate [14C]22:5(n-3), the process appears to be qualitatively different from that of retinoblastoma cells.

Chain elongation of polyunsaturated fatty acids by vascular endothelial cells: studies with arachidonate analogues

This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2-72 hr in medium supplemented with 0.9-2.6 microM [14C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation of naturally occurring C20 polyunsaturated fatty acids occurred with eicosapentaenoate (20:5(n-3] greater than Mead acid (20:3(n-9] greater than arachidonate (20:4(n-6]. Chain length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18:4 greater than 19:4 greater than 20:4 greater than 21:4); effects of initial double bond position were also observed (6,9,12,15-20:4 greater than 4,7,10,13-20:4. Neither 5,8,14- nor 5,11,14-20:3 was elongated to the extent of 5,8,11-20:3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal percentages of elongation, suggesting that the content of cellular C20 and C22 fatty acids may represent a balance between chain elongation and retroconversion. Umbilical vein endothelial cells do not exhibit significant desaturation of either 22:4(n-6) or 22:5(n-3). By contrast, incubation with 5,8,11,14-[14C]18:4(n-4) resulted in formation of both [14C]20:5(n-4) and [14C]22:5(n-4). The respective time courses for the appearances of [14C]22:5(n-4) and [14C]20:5(n-5) suggests delta 6 desaturation of [14C]22:4(n-4) rather than delta 4 desaturation of [14C]20:4(n-4).

High-density-lipoprotein-induced cholesterol efflux from arterial smooth muscle cell derived foam cells: functional relationship of the cholesteryl ester cycle and eicosanoid biosynthesis

Eicosanoids have been implicated in the regulation of arterial smooth muscle cell (SMC) cholesteryl ester (CE) metabolism. These eicosanoids, which include prostacyclin (PGI2), stimulate CE hydrolytic activities. High-density lipoproteins (HDL), which promote cholesterol efflux, also stimulate PGI2 production, suggesting that HDL-induced cholesterol efflux is modulated by eicosanoid biosynthesis. To ascertain the role of endogenously synthesized eicosanoids produced by arterial smooth muscle cells in the regulation of CE metabolism, we examined the effects of cyclooxygenase inhibition on CE hydrolytic enzyme activities, cholesterol efflux, and cholesterol content in normal SMC and SMC-derived foam cells following exposure to HDL and another cholesterol acceptor protein, serum albumin. Alterations of these activities were correlated with cholesterol efflux in response to HDL or bovine serum albumin (BSA) in the presence or absence of aspirin. HDL stimulated PGI2 synthesis and CE hydrolases in a dose-dependent manner. Eicosanoid dependency was established by demonstrating that HDL-induced acid cholesteryl ester hydrolase (ACEH) activity was blocked by aspirin. CE enrichment essentially abrogated HDL-induced PGI2 production in cells which also exhibited decreased lysosomal and cytoplasmic CE hydrolase activities. In CE-enriched cells whose cytoplasmic CE pool was metabolically labeled with [3H]oleate or cLDL containing [3H]cholesteryl linoleate, aspirin did not alter HDL- or BSA-induced net CE hydrolysis or efflux, respectively. Finally, aspirin treatment did not alter the mass of either free or esterified cholesterol content of untreated or CE-enriched SMC following exposure to acceptor proteins. These data demonstrated that CE enrichment significantly reduced HDL-induced activation of CE hydrolytic activity via inhibition of endogenous PGI2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroperoxides produced by n-6 lipoxygenation of arachidonic and linoleic acids potentiate synthesis of prostacyclin related compounds

In a previous paper we reported that arachidonic acid (20:4(n-6] strongly enhances the endothelial cell synthesis of prostaglandin I3 (PGI3) from eicosapentaenoic acid (20:5(n-3], in stimulating the cyclooxygenase rather than the prostacyclin synthase (Bordet et al. (1986) Biochem. Biophys. Res. Commun. 135, 403-410). In the present study, endothelial cell monolayers were co-incubated with exogenous 20:5(n-3) or docosatetraenoic acid (22:4(n-6], and n-6 lipoxygenase products of 20:4(n-6) or linoleic acid (18:2(n-6], namely 15-HPETE and 13-HPOD, respectively. Prostaglandins or dihomoprostaglandins were then measured by gas chromatography-mass spectrometry. Both hydroperoxides, up to 20 microM, stimulated the cyclooxygenation of 20:5(n-3) and 22:4(n-6), in particular the formation of PGI3 and dihomo-PGI2, respectively. Higher concentrations inhibited prostacyclin synthetase. In contrast, the reduced products of hydroperoxides, 15-HETE and 13-HOD, failed to stimulate these cyclooxygenations, 13-HPOD appeared more potent than 15-HPETE and the cyclooxygenation of 22:4(n-6) seemed to require higher amounts of hydroperoxides to be efficiently metabolized than 20:5(n-3). These data suggest that prostacyclin potential of endothelium might be enhanced by raising the peroxide tone.

Docosahexaenoic acid metabolism and effect on prostacyclin production in endothelial cells

Bovine aortic endothelial cultures readily take up docosahexaenoic acid (DHA). Most of the DHA was incorporated into phospholipids, primarily in ethanolamine and choline phosphoglycerides, and plasmalogens accounted for 34% of the DHA contained in the ethanolamine fraction after a 24-h incubation. The retention of DHA in endothelial phospholipids was not greater than other polyunsaturated fatty acids and unlike arachidonic and eicosapentaenoic acids, DHA did not continue to accumulate in the ethanolamine phosphoglycerides after the initial incorporation. About 15% of the [14C(U)]DHA uptake was retroconverted to docosapentaenoic and eicosapentaenoic acids in 24 h. Some of the newly incorporated [14C(U)]DHA was released when the cells were incubated subsequently in a medium containing serum and albumin. The released radioactivity was in the form of free fatty acid and phospholipids and after 24 h, 11% was retroconverted to docosapentaenoic and eicosapentaenoic acids. Total DHA uptake was decreased only 10% by the presence of a 100 microM mixture of physiologic fatty acids, but as little as 10 microM docosatetraenoic acid reduced DHA incorporation into phospholipids by 25%. DHA was not converted to prostaglandins or lipoxygenase products by the endothelial cultures. When DHA was available, however, less arachidonic acid was incorporated into endothelial phospholipids, and less was converted to prostacyclin (PGI2). Enrichment of the endothelial cells with DHA also reduced their capacity to subsequently produce PGI2. These findings indicate that endothelial cells can play a role in DHA metabolism and like eicosapentaenoic acid, DHA can inhibit endothelial PGI2 production when it is available in elevated amounts.

Sertoli-cell prostaglandin synthesis. Effects of (follitropin) differentiation and dietary vitamin E

The synthesis of prostanoids by the Sertoli cell was assessed as part of a study on the role of vitamin E in maintaining spermatogenesis. Analyses of eicosanoid synthesis from endogenous substrate were carried out using freshly isolated Sertoli-cell-enriched preparations from both pre-pubertal and adult rats fed purified diets with and without vitamin E, as well as cells carried in primary culture. Freshly isolated cells from both the immature and fully differentiated adult testes produced PGI2 (prostaglandin I2) and PGE2, but PGF2 alpha was produced only by cells of the adult vitamin E-deficient rat. Cells from adult controls synthesized PGF2 alpha after primary culture. In contrast with other hormone responses of this cell, which are refractory in the adult, FSH (follitropin) potentiated prostaglandin production by freshly isolated cells of both immature and adult rats. The FSH response of Sertoli cells from immature animals did not change after primary culture. Adult cells were refractory to the hormone after culture, but the total amounts of prostaglandins produced by these cells were 10-fold higher than by either freshly isolated or cells of the immature in culture. Analogues of cyclic AMP did not potentiate prostaglandin synthesis. However, mepacrine, a phospholipase inhibitor, blocked the FSH effect. The finding that Sertoli cells synthesize prostaglandins and FSH enhances prostaglandin production implicates a potential role for eicosanoids in spermatogenesis and suggests that vitamin E may affect intratesticular regulators.

Elongation of C20 polyunsaturated fatty acids by human skin fibroblasts

Human skin fibroblasts actively elongate a portion of incorporated C20 polyunsaturated fatty acids to their respective C22 derivatives. As much as 40% of incorporated [14C]eicosapentaenoate is elongated within 8 h and 85% by 48 h. Elongation of [14C]arachidonate is initially less than half that of [14C]eicosapentaenoate and plateaus at 20-30% of incorporated 14C-labeled fatty acid. The elongation of 5,8,11-[14C]eicosatrienoate is intermediate between that of 20:4(n-6) and 20:5(n-3). Docosatetraenoate is not an effective inhibitor of the elongation of arachidonate, thus suggesting that the observed plateau is not due to product inhibition. When concentrations of exogenous fatty acids are increased, these cells elongate substantial quantities of C20 polyunsaturated fatty acids; elongation of eicosapentaenoate is consistently more extensive than that of arachidonate. Eicosapentaenoate is also an effective inhibitor of the elongation of [14C]arachidonate. Increases in exogenous arachidonate up to 10 microM result in an increase in elongation of [14C]arachidonate both in absolute quantities and as a percentage of that incorporated; the arachidonate thus acts as a positive modulator of its own elongation. Increased eicosapentaenoate also enhances the elongation of [14C]eicosapentaenoate, but only at lower concentrations (0.02-0.15 microM). The factors which regulate the elongation of C20 polyunsaturated fatty acids in human skin fibroblasts serve to permit extensive elongation of eicosapentaenoate while retaining incorporated arachidonate primarily in its C20 form.